The present invention relates to a washing apparatus and washing method for washing semiconductor wafers and the like.
As integration of semiconductor wafers and the like has increased in recent years, circuit wiring has become microsized, and accordingly dust particles present on wafers and the like must be reduced; that is, there is a need for super-cleaning.
Such super-cleaning of semiconductor wafers and the like is difficult to achieve through a single washing step during a washing operation of the semiconductor wafers and the like. Therefore, it has been the practice in a conventional process for washing semiconductor wafers and the like to provide a plurality of washing apparatuses which are used to clean residue dust off the surfaces of the semiconductor wafers and the like by washing them a plurality of times so as to achieve super-cleaning.
In other words, in the case of washing a semiconductor wafer which has been polished by means of a polishing device, for example, a plurality of roll type washers as shown in FIG. 3 are arranged in a side by side configuration, together with a spin dryer (not shown).
The roll type washer as shown comprises a plurality (six in the drawing) of spindles 11 (a retaining member having a rotary-drive mechanism) which rotate while supporting an outer circumference of disk-shaped semiconductor wafers W, two roll type members 13 and 15 respectively arranged above and below the semiconductor wafer W, driving mechanisms 17 and 18 which actuate roll type members 13 and 15 to move vertically and rotate in the directions of arrows F1 and F2, and a washing liquid dispensing nozzle 19 which may feed a washing liquid (ultra-pure water) onto the surface of semiconductor wafer W. Although omitted in the description to be made hereinbelow, the roll type washer also comprises a nozzle for feeding washing water to the rear surface of the wafer W. Although the roll type members 13 and 15 are formed from PVF (porous polyvinyl formal) sponge-material on their surfaces, it may be alternatively possible to use a foamed polyurethane, a nylon brush or a mohair made of nylon to form the roll type members.
In order to wash the semiconductor wafer W by means of this roll type washer, the outer periphery of the semiconductor wafer W is contained in and brought into contact with circumferential grooves 12a which are defined in tops 12 of spindles 11, and the semiconductor wafer W is caused to rotate in the direction of the arrow E substantially at a constant speed by spinning tops 12 at the same speed. In the meantime, the semiconductor wafer W is positioned such that its surface to be polished is oriented upwardly.
Then, members 13 and 15 are brought into abutment with upper and lower surfaces of the semiconductor wafer in such a manner that the members sandwich the semiconductor wafer therebetween, and simultaneously a washing liquid is injected or caused to fall through washing liquid dispensing nozzle 19.
Thus, dust particles which adhere to the upper and lower surfaces of the semiconductor wafer W are scraped away by means of roll type members 13 and 15, and then flow away together with the washing liquid.
The roll type members 13 and 15 have large surface areas (that is, large contact areas against the semiconductor wafer W). Thus, they provide optimum washing of semiconductor wafers, which have been polished by means of a polishing device and upon which a great deal of dust particles have been deposited, while simultaneously ensuring a long operational life.
The semiconductor wafer W which has been washed is repeatedly washed by means of second and subsequent roll type washers in a similar fashion, and then dried in a spin dryer (not shown). In the meantime, the lower roll type member 15 optionally may be omitted, if so required.
The prior art technique as above-described has suffered from several problems which will be described hereinbelow.
(1) In the roll type washers in the above-described prior art arrangement, the outer peripheral speed of the roll type member is constant at all portions thereof. But, since the peripheral speed of the wafer becomes progressively slower toward the central portion thereof, a relative speed between the roll type member and the semiconductor wafer W becomes progressively slower toward such central portion. Accordingly, the dust removal capability of the member is reduced at the central portion of the wafer W in comparison with the capability occurring at the outer periphery of the wafer. Thus, there is a tendency that dust may be left around the central portion. Also, dust which is not removed by the primary washer may not be removed by second and subsequent washers.
(2) Since the semiconductor wafer W is rotated by rotation of tops 12, and when the tops 12 rotate at a substantial high-speed, the semiconductor wafer W may slip, preventing it from turning at a correspondingly high-speed. Moreover, the circumferential grooves 12a in the tops 12 can become worn to thus generate dust particles. Therefore, the semiconductor wafer W may not be washed efficiently. The wafer is rotated for practical purposes at a speed of about 300 rpm, and should preferably be rotated at the speed of about 100 rpm.
This roll type washer cannot be used as it is without modification in the spin dryer in which the semiconductor wafer must be spun at a speed over 2000 rpm, for example. Thus, when this roll type washer is arranged in plural numbers, another spin dryer must be provided additionally, thereby increasing dimensions of the washing installation itself.
The semiconductor wafer W is arranged to be rotated around its own axis with its outer periphery in contact with the tops 12 since the roll type washing members 13 and 15 are arranged to span the diameter of front surface and reverse surface of the semiconductor wafer W. Thus, the wafer W can be washed while the members are constantly kept in contact not only with opposite surfaces of wafer W, but also with the peripheral portion of the wafer W, without making contact with the tops 12 and the spindles 11.